The background of this invention pertaining to the detection of discontinuities in a flowing fluid stream is fully set forth in my U.S. Pat. Nos. 4,112,773, and 4,214,484, both hereby incorporated by reference. The background pertaining to obtaining information about the composition of the fluid is set out in my U.S. patent application Ser. No. 136,169, filed Mar. 31, 1980, now abandoned, also hereby incorporated by reference.
It is desirable to increase the signal-to-noise ratio in pulse-echo search units by eliminating spurious acoustic signals which might be detected by the unit. One source of such spurious signals is random sound waves generated by the units themselves, which random waves enter the material adjacent to the unit, and eventually reflect back to the unit thereby interferring with the unit's ability to detect information-carrying signals.